The present invention relates to a member for supporting an optical fiber coupler used for separating, coupling, branching or combining light signals in an optical fiber communication system while preventing any damage of the optical fiber coupler.
An optical fiber communication system in general makes use of an optical fiber coupler as an important elemental part for separating, coupling, branching or combining light signals transmitting through the optical fibers. Such an optical fiber coupler is disclosed in, for instance, Japanese Patent Provisional Publication No. 63-271208. The optical coupler disclosed in this patent is produced by bundling a plurality of optical fibers arranged parallel to one another, welding these fibers together through heating and then drawing the welded fiber bundle so as to have a tapered welded portion having a small diameter. The tapered portion of small diameter serves to separate, couple, branch and/or combine the light signals passing through the optical fibers.
The optical fiber coupler thus produced has a low mechanical strength at the welded portion of small diameter. Moreover, the performance characteristics thereof is unstable since it suffers from changes in various properties such as coupling ratio of light signals when only a low external force is applied to the welded portion of small diameter. For this reason, there has been proposed a structure or method for reinforcing the optical coupler which comprises adhering both ends of the welded thin portion of the optical coupler to a tool and accommodating the assembly in a body of equipment (see, for instance, the aforementioned patent).
However, it has been found that the use of such a reinforcing structure often accompanies an excess loss of light signals passing through the optical coupler. The inventors of this invention have investigated the cause of this drawback in detail and come to the following conclusions. In the reinforcing structure disclosed in the foregoing Japanese Patent Provisional Publication, the optical coupler is partially adhered and fixed to the tool by an adhesive and the portions of the optical fibers other than those adhered to the tool are suspended within a space. For this reason, the axes of the optical coupler and the tool deviate from one another due to slight deviations between the positions thereof to be placed during adhesion, slight deviation therebetween due to contraction during hardening the adhesive and deviation therebetween due to the difference between the thermal expansion coefficients of these two components observed during heat cycles. Such deviation between the axes of the optical coupler and the tool would become a principal cause of the foregoing excess loss.
In addition, the optical coupler of the foregoing patent is accommodated in a body of equipment after adhering it to the tool. This results in the scaling up of the reinforcing structure.